Pulse operated gaseous electron tube circuits



Sept. 16, 1952 l. WOLFF Filed Feb. 24, 1951 PULSE OPERATED GASEOUS ELECTRON TUBE CIRCUITS PULSE SOURCE will INVENTOR Irvmg off-P ATTORNEY potential.

Patented Sept. 16, 1952 PULSE OPERATED GASEOUS. ELECTRON TUBE CIRCUITS Irving Wolff,1I.rinccton, N. .L, assignor to Radio Corporationof America, a corporation of Delaware Application February 24, 1951, Serial No..2l2,632

The present invention relates to improvements in gaseous electron tube systems and particularly to a method of and an apparatus for operating a gaseous electron tube under conditions such that a relatively high current can be passed through the tube at a potential less than that required to ionize the tube gas.

In a conventional vacuum tube, a control grid placed between the cathode and the anode provides a very eflicient means of controlling the tube current. A very small change in the control grid potential will have a relatively large effect on tube current, it being possible to vary the tube current smoothly and continuously,

within relatively wide limits by varying the control grid potential.

Vacuum tubes, however, are subject to certain limitations clue to space charge effects, and usually require high operating potentials. It'has been found that these limitations can be overcome by adding asmall quantity of gas to the tube and ionizing the gas. If a sufiiciently high potential is' applied between an emitting and a collecting electrode in the tube, the gas will become ionized by electron bombardment of the gas-molecules, thereby developing positive ions which will neutralize the negative space charge of the electron stream. The combined cloud or plasma of. ions and electronswill act as an excellent conductor, allowing the tube current to riseveryrapidly until the full electron emitting capacity" of the emitterv electrode is being utilized.

In the case of the conventionally operated gas tube, however, it found. that a control electrode has only a trigger type. oi control action. A predetermined negative potential on the control electrode will prevent tube current iromflowing. The tube current flow can. be started by a suitable decrease in this negativecontrol electrode However, once the tube begins to conduct, the control electrode loses practically allcontrol and the tube current becomes independent of the control electrode potential.

In addition to the loss of contr.ol bythe control electrode, the conventionally operated gas tube presents a further problem. That is, in

general, a certain amount of energy must be 7 Claims. (01. 25.0 -36) givento an, atom or molecule in. order to cause anelectron to, be liberated, fromthe energy confines of the atomic structure. In, the case of a gastube, this means that'the bombarding electronsmust be. given a certain minimum velocity in order to, provide this minimum, amountof energy andthus cause ionization. To give the ionizing electrons this minimum velocity, a minimum potential. or are drop must be maintained. between the electron emitting electrode and an electron collecting electrode immersed in the gas; This are drop represents wasted voltage, and, is particularly objectionable in any system. where voltage is to be transferred from a source to a load through a gas tube transfer circuit with the least possible voltage loss inthe transfer. circuit. i V In a copending application. of E. O'. Johnson, Serial No. 185,745, filed September 20, 1950, and assigned to the assignee of the present invention,

there is described and claimed a gaseous; electron tube in which the functions of supplying energy to provide a space charge neutralizing plasma, and of providing a field to draw' work current through the plasma, are: separated. -With a'low work circuit energizing potential, it was. found that the functionv of providing plasma would not be taken over by the'work circuit. Since: the work current is incapable of causing ionization, an auxiliary source of" ionizing current is. provided to. fill" the need. I

In such. a tube structure, it is found that a very high. current can be; passed between the main emitter electrode and the collector electrode at potentials far below those required to i'onize the" gas.

"It'i's also found that the" current: flow between th'elmain emitter electrode and the collector electrode can'bei controlled. in various ways, one of which is by varying' the potential of: a control electrode as in a conventional vacuum tube. It is an object of. this invention to provide an improved method of and an apparatus for operating gaseous electron tubes which are-capable of continuous control grid action.

It is a further object of this invention to provide a gaseous electron tube circuit which/is operative from a source of potential having. a magnitude which is less than that required to cause ionization of the tube gas.

It is a still further object of this invention to provide a gaseous electron tube circuit which is capable of sustaining ionization by means of the application of A.-C. or D.-C. voltage pulses tothe ionizing circuit. I a

1 It another object of this invention to provide a gaseous electron tube oscillatory circuit which is operable from a source of potentialoi amplitude less than that required to cause ionization of the tube gas. I

' In' accordance with" the' present invention, 55

there is'provided a system wherein space'cl'iarge neutralizing ions are generated in a gaseous electron tube by the application of discrete intervals of a potential sufficient to cause ionization of the gas. In accordance with a preferred embodiment of the invention, there is provided an oscillatory circuit and a feedback arrangement such that once the oscillatory circuit has been placed in operation, pulses of sufiiciently high potential to cause and sustain ionization will be fed back to the ionizing circuit.

A more complete understanding of the present invention can be had by reference to the following description of illustrative embodiments thereof, when considered in connection with the accompanying drawing, wherein:

Figure 1 is a schematic diagram of a gaseous electron tube system illustrating the general principles of the present invention;

Figure 2 is a view in cross section of a type of gaseous electron tube suitable for use in accordance with the present invention; and

Figure 3 is a circuit diagram of a loudspeaker operating system embodying the present invention. r

In the system shown in Figure 1, there is provided a gaseous electron tube l having an anode I 2, a control grid [4, a main cathode IS, an auxiliary cathode I 8 and a focussing electrode 20. Structural details of the tube I 0 are given hereinafter. There is connected between the main cathode l 6 and the auxiliary cathode l8, a pulse source 22, which may be any convenient source of pulses providing a peak potential or pulse amplitude suflicient to cause ionization of the tube gas. A work circuit 24, such as an oscillatory circuit, an amplification circuit, a control circuit or any other conventional circuit for operation with an electron tube, is connected between the anode l2 and a voltage source designated B+.

It has been found that when a gas tube such as the tube I0 is connected as shown, with a pulse source of suflicient amplitude to cause ionization being connected between two spaced electrodes thereof (e. g., the main cathode l6 and the auxiliary cathode H! of the tube [0), there will be created and maintained within the tube envelope an eifectively continuous plasma, provided the amplitude and repetition rate of the applied pulses is sufilciently high. .It is, of course, to be understood that the minimum pulse amplitude and repetition rate required to provide a continuous plasma will be determined by the tube geometry, and the particular type and'pressure of gas utilized.

Once plasma is provided within the tube envelope, it has been found that the work section of the tube I0 (comprising the anode [2, the conof the tube are unusually high. The work section of such a tube can be made to handle currents of the order of amperes depending, of

course, upon the tube geometry and the type of gas utilized. 7

One type of gas tubesuch as may be utilized in accordance with the present invention is shown in'cross-section in Fig. 2. Tubes of this type are described in greater detail and claimed in the above-identified copending application of E. 0. Johnson.

In the tube shown in Fig. 2, a gas tight envelope I0 is provided with a main cathode [6. A U-shaped control electrode or grid l4 and a U-shaped anode l2 partially surround the oathode I6.

Opposite the open ends of the grid l4 and the anode l2 there is mounted a cylindrical focussing electrode 20, provided with an elongated slot 21 facing the open ends of the grid and anode structures. An auxiliary cathode I8 is mounted coaxially within the focussing electrode 20.

A tube having a structure such as that shown in Fig. 2 can be operated as follows:

If a voltage greater than the ionizing voltage of the gas in the tube is applied between the auxiliary cathode l8 and the anode I2, a current will flow which will ionize the gas in the tube. As a result, a highly conductive mixture or plasma of ions and electrons will be created within the tube envelope. The focussing electrode 20 is effective to concentrate the ionizing current, making it possible to obtain high plasma densities with very small amounts of current or power. With the tube gas ionized to create plasma in the mannerjust described, it becomes possible to pass a relatively high current between the main cathode and the main anode with a voltage drop which may be of the order of 0.1 volt or less. Furthermore, it becomes possible to control this main cathode-anode current by means of a control electrode I 4 disposed in the space path as shown. 7 In some instances, the focussing electrode is utilized to control the ionizing current in order to control the main tube current. When an A.-C. or D.-C. pulse potential source of sufficient magnitude is connected between the auxiliary cathode IB and the main cathode I B, a plasma will be generated within the envelope of the gas tube 10. Once the plasma has been generated, the work circuit section will operate as a grid-controlled, very low impedance section. It hasbeen found that potentials applied to the control grid M will provide control of the work circuit current in the same manner as the grid control provided in the conventional vacuum tube.

The circuit diagram of Figure 3 shows an oscillator circuit witha gas tube l0, similar to the gas tube 10 illustrated in Figures 1 and 2, for energizing another. like tube 60, used as anamplifier. The oscillator portion of thecircuit comprises a pair of inductors 26 and 28 which are inductively coupled to each other andwhich are respectively connected to the anode l2 and to the control grid I4 of the tube In. A capacitor 30 is connected in shunt with the inductor 26 to provide a resonant circuit at any suitable operating frequency. Tests have shown that frequencies as low as sixty cycles or as high as frequencies in the radio range can be employed. A source of direct-current potential, shown as a battery 32 shunted by a bypass capacitor 34, is connected between a point of fixed reference potential, such as ground, and the tuned resonant circuit 26, 30 to provide directcurrent energizing potential for the gas tube Hi.

In order to provide proper operating bias for the control grid M, a high resistance resistor 36 and a shunt connected by-pass capacitor 38 are connected between one end of the grid in- The battery 32% is; connected: to. the;.tuha.- I- ll by aij'switch comprising. a: pair of. contact; arms: 42 and 14.4 and: a1. plurality of: fixed. contacts I. 46;. &8; 5.8; Stan-did, When .thec'ontact. armsfliand 44':

are-.moved to the extreme right; theyw-ill engage the-fixed contacts 48- and 5.4; respectively; which will provide. an open circuit for the, battery '32i As: the contact: arms: 42' and 44.. are; moved .to. the

leftrto the. position shown in Figure3, the con.-

tactarm: Ma first? will provide. a closed electrical circuit? for a starting. inductor 56 which is: con:- nected':between;the=fixed contact 521' and-ground. Asthis. electrical circuitis: completed, current will clarity; thersecond tube. 6.0 ln liig-uredit will beireferred: to by: different reference/numerals from those used' toirefer'to: the other gas tubes illustrated in the drawing. It is to be understood; however, that thisstube ispreferabliv: of the same. type; as: illustrated in, other; portions: of

' the control grid It and ground, sos'thatIinp-ut flow through the. starting: inductor-56r .When

the switch is: moved further: to the left-to break thecircu-it through theinductor 5fig'anind-uced voltage will beset up inan ionization inductor 581'which is inductively" coupled to the starting It is, of course, to. be understood inductor 55:; that the electrical circuit: of the startinginductor 56is completed only momentarily, as by a switch wiping movement. Accordingly, the. changeof current through the starting-inductor 56 will pro.- duce in the ionization inductor '58'1a-rel'ative1y large induced potential having a peak I amplitude sufii'ciently. high to cause ionization of the tube gas; At the same time, the other contact arm 42 will remain in engagement with the fixed contact 46 which is connected to the anode IZ'of the tube It).

The ionization inductor 58 is connected between the auxiliary cathode I8 of the tube In and gr-ound; Therefore, as current is: caused to flow through the starting inductor 56, the. in-

duced voltage which is developed in theinductor 58' will'beapplied between the auxiliary-cathode l8 and ground. Since themain cathode l6 of the tube It! is connected directly to ground; this induced potentialis in effect applied between the maincathode Iii and theauxiliary cathode 18' of the gas tube 10.. Thus,'if the induced volt-age is of sufficient magnitude, an ionizing dischargewill occur between the main cathode lli' and the auxiliary cathode 18 of the tubelfl. Upon ionizationxofxthe gas in the tube Imthe. oscillator "portion of. theitube will become operative as a low impedance oscillator.

Oscillatory currentsflowing inthe oscillator-ind'uctors' 26, 28'will inducea pulsatingrvoltagelin the inductor 58, which is inductively coupled to the oscillator-inductors 2.6 and 28.. Thisvoltage induced in the inductor 58=may be the sameas or a harmonic of" the oscillator frequency.- The voltage pulses induced in the inductor 58 readily can be made to be of sufiicient magnitudesto cause ionization of. the tubegas; If these. induced pulses are applied at a suflicientlyhigh, rate, the plasma will have not had-enough time, between pulses to decay below the densityrequired. to sustain the work circuit current. If'the plasma decay is prevented in this manner, the triodesection of the tube ID will be continuously immersed in a highly conductive plasma and will operate as though plasma were being generated constantly within the tube.

It is, of course, tobe understood that the oscillator circuit illustrated in. Figure 3 of the draw ingis merely representative; and that. other well known oscillator circuits could as well be employed in the same. manner.

It has also been found that a gas tube energized in themanner disclosed herein can be used to directly drive the voice coil of a'loudspeaker because .of' the low eiiectiveimpedance of the work.- circuit section of thetube. Forthe sake of signals can be applied across the. resistor-Fad througha capacitor 'H and aupair. of terminals 12 The: work circuit of: the tube. 60-. iscompleted by: connecting: the main cathode M: directlyto ground;

Ionizing pulses are applied between; the main cathode 14 and the auxiliary cathode l5 oivthe,

tube. 69' from the ionizing inductor '58. Of. course,

this pulse source arrangement :is purely .illusatrative; as any suitable pulse source'may: bacon;

nectedz. between. the. main and auxiliary-cathode of" the.tuloe-.6fl. When itisnot desired to :utilize the focussingelectrode 1.8 as a separate control electrode;-. it may be connected to thecathode lfiqasshown.

As previously described, when pulsesqot sufficient amplitude and repetitionrrateare applied between the main cathode M and the auxiliary cathode Id of the-.tube. 68, a. plasma will be gen erated within the tube which will provide;. a; COIL-1 ductive path between. the other electrodes; im: mersed in the. plasma. Signal j potentials applied between. the. control, grid 10 and. ground will. be efiective; to. control the; work currentflowing: be,- tweenthemain cathode M and the anodeld It has been. found; that. this control is uninterrupted, andis sufiiciently linear to provide substantially distortionlessoutput from thelcudspeaker 64.

It. will be understood that the triodesection comprising the cathode T4, the control grid; l'0 andthe anode 66 of the, tube 66 can Joe utilized as. at current contrcldevice for. anelectric; motor, or; for: any other purposes for which an electron tube is appropriate:.;

Inthe-above; discussion, it has been stated that the; repetition. rateoi the. pulses applied; to. the iomzation. circuitv should. be, sufliciently high, to preventrappreciable; decay of the plasma within the tube envelope. Of course, thepulserepetie tion rate might be less than; that, required, to maintain an uninterrupted plasma. Under these circumstances, howeventhe, triode or-qwork circuit. section of the". tube willnot provide a con;-

tinuously low impedance-path for the. work: Ojlrcuit current. If, in a. special applicatiomitiis desired that the work: current be allowed torflow freely only in. pulse fashion; it. is: within: the purview of; the presentinvention to. use; a. feed;- back-x-pulse arrangement of the type.- disclosed herein as the ionizing pulse source. 1 1

Itwillbe appreciated that pulseoperation of a gaseous electron tube, as providedby this: in;- vention, is predicated only upon the application: of' pulse energy from asource other than that utilized to energize the workcircuit, and" not on a particular configuration ofelectrodes: That is; ionizingpulses of alternating.voltage'can be applied toa pair of external electrodes, for example; which: areso arrangedas to establish-a pulsed alternating field through the tube gas. It

has'been foundthat when discrete pulses of high frequency energy are; appliedby:- means of such external electrodes,-plasma" generation occurs within'the tube gas in substantially the same manner as though the energizing field were established within the confines of the tube envelope.

Due to the inductive kick arrangement provided by the coupled inductors 56 and 58, it is possible to use as an energizing source a battery 32 of potential less than that required to cause ionization of the gas in the tube I0. After ionization has occurred and the oscillator portion of the tube I is oscillating freely, the potential required to cause ionization is provided by the oscillator circuit through the inductively coupled ionization inductor 58. There is thus provided agas tube circuit which may be operated from a voltage source as low as six volts and which may provide in its output circuit alternating current voltages in the order of 100 volts and more.

It should be-clear from the above discussion that the present invention provides a means for and a method of operating a continuously controlled-gas tube with a source of energizing potential less than that required to ionize the gas, as well as a means for and method of maintaining continuous conduction in the work circuit of the tube by pulsing the ionization circuitfrom a suitable pulse source.

What is claimed is:

1. The method of controlling a flow of electrons from an electron emitter to the electron collector electrode in a gas filled electron tube having a pair of emitter electrodes and a collector electrode, said method comprising the steps of impressing voltage pulses of amplitude sufiicientto ionize the tube gas between said air of electron emitter electrodes, impressing a separate potential between one of said emitter electrodes and said collector electrode, and impressing a variable control potential between one of said electron emitter electrodes and an electrode adjacent to said one electron emitter electrode.

2. A gas tube system comprising a gas filled electron tube having an anode, a main cathode and an auxiliary cathode, a source of voltage pulses of amplitude sufficient to ionize the gas in said tube, a circuit connecting said voltage pulse source between said main cathode and said auxiliary cathode to ionize the gas in said tube in periodic bursts, a load device, and a circuit separate from said first named circuit connecting said anode to said main cathode through said load device. -3. A gas tube system comprising a gas-filled electron tube having an anode, a control grid, a main cathode and an auxiliary cathode, a source of voltage pulses of amplitude greater that that required to ionize the gas in said tube, said pulse source being connected between said main cathode and said auxiliary cathode, a voltage source, a work circuit connecting said main'cathode to said anode through said last named voltage source, and means to control the voltage on said control electrode.

4; In a circuit of the type comprising a gaseous electron tube having a plurality of electrodesineluding an anode, a control grid, a main cathode and an auxiliary cathode, the combination of a pair of oscillator inductors respectively electrically connected with said control grid and said anode, a source of energizing potential connected vto said anode inductor and being capable of providing a potential less than that required to cause ionization of the tube gas, and a feedback inductor coupled with said oscillator inductors and'electrically connected to said auxiliary cathode'to provide "between said auxiliary cathode and said main cathode voltage pulses of amplitude sufficient to causeionization of the tube gas.

5. In a circuit of the type comprising a gaseous electron tube having a'plurality of electrodes including a grid controlled section and an auxiliary cathode, the combination of a switch having a. plurality of fixed contacts and a pair of'movable contact arms, an oscillatory circuit including an inductor coupled between said grid controlled section and one of saidcontacts, a feedback inductor inductively coupled with said oscillatory circuit inductor and connected between said auxiliary cathode and a point of fixed reference potential, a source of energizing potential less than that required to cause ionization of the tube gas, said source of potential being connected between said switch contact arms and said point of fixed reference potential, and a starting inductor inductively coupled with said feedback inductor and connected between another-of said switch contacts and said point of fixed, reference potential, the arrangement being'such that movement of said contact arms, to respectively engage said one contact continu-' ously and said other contact temporarily, will energize said starting inductor and cause a potential suificient to ionize the tube gas to be applied between said auxiliary cathode and another of said electrodes.

6. In a circuit of the type utilizing a gaseous electron tube including an anode, a control grid, a main cathode and an auxiliary cathode, the combination of a switch having a plurality of fixed contacts and a pair of movable contact arms, a tuned resonant circuit connected between said anode and one of said switch contacts, an oscillator inductor connected to said control grid and inductively coupled with said tuned resonant circuit, a feedback inductor inductively coupled with said oscillator inductor and connected between said auxiliary cathode and a point of fixed reference potential, a source of energizing potential, less than that required to cause ionization of the tube gas, connected between said pair of movable contact arms and said point of fixed reference potential, and a starting inductor'inductively coupled with said feedback inductor and connected between another oneof said switch contacts and said point of fixed reference potential so that movement of said contact arms, to sequentially engage said contacts, temporarily will energize said starting inductor and cause a potential sufficient to ionize the tube gas to be developed by said feedback inductor.

7. In a circuit comprising a gaseous electron tube having a plurality of electrodes including a grid controlled section and an auxiliary cathode, the combination of a switch including a pair of contacts and a pair of contact arms, said pair of contacts being so positioned relative to said respective arms that one of said pair of arms continuously engages one of said contacts while simultaneously the other of said pair of arms temporarily engages the other of said pair of contacts, an oscillatory circuit including an inductor connected between said grid controlled section and said one contact, an output circuit coupled to said oscillatory circuit, a feedback inductor inductively coupled with said oscillatory inductor and connected between said auxiliary cathode and a point of fixed reference potential, ia source of energizing potential less than. that required cause ionization of the tube gas, said source being connected between said oscillatory '1 circuit inductor and said point of fixed reference 1 potential, and. a starting inductor inductively coupled with said feedback inductor and OOH-H nected between said other switch contact and; said point of fixed reference potential wherebyi; movement of said contact arms, to respectively'f engage said one contact continuously and to engage said other contact temporarily will connect said source of potential to said oscillatory} circuit continuously and to said starting inductor" Number 10, temporarily to produce in said feedback inductor V a potential sufficient to ionize the tube gas.

IRVING WO-LFF.

REFERENCES CITED The following references are of record in the 5 file of this patent:

UNITED sTA f s PATENTS Name Date 2,130,191 Meier Sept. 13, 1938 2,158,564 Meier May 16, 1939 2,213,551 Nelson Sept. 3, 1940 

